The present invention relates generally to electrical wiring devices, and, more particularly, to electrical outlet receptacle devices of improved construction, having an automatic grounding system for grounding the device to a grounded electrical outlet box without requiring a metallic mounting strap and improved mounting means for ensuring proper mounting of the device adjacent an opening formed in a wall member.
Electrical outlet receptacles for residential, hospital and industrial use are well known in the art. Hospital and industrial grades of receptacles are often made in specialized configurations or with heavy duty features in order to satisfy various code requirements (e.g., Underwriters' Laboratories Hospital Grade Test Program). Residential grade receptacles, on the other hand, are generally required to satisfy somewhat less stringent U.L. requirements and have been manufactured for years with little or no design changes so as to sell at the lowest possible cost. For example, residential grade outlet receptacles are often made with a body and cover member made from a thermo-set material using the same type of compression molds which have been in use for decades. These devices also incorporate steel mounting straps which require separate copper alloy ground contacts for mating with the ground prong of a plug inserted into the device.
Although known prior receptacle devices have provided generally satisfactory results over the years, they do suffer several disadvantages. For example the typically used thermo-set materials are relatively brittle and are susceptible to cracking or breakage during fabrication or installation. In addition, the metal mounting strap (which is either sandwiched between the receptacle body and cover or wrapped around the device) is also a source for additional fabrication, assembly and handling problems. For example, the mounting straps are typically made of steel which is susceptible to corrosion. In addition, the strap is easily deformed during fabrication and handling. Moreover, steel straps cannot directly form the ground contacts for a receptacle. Rather, separate grounding contacts made of the proper copper alloy material must be electrically connected to the mounting strap, either by riveting or pressure fitting. This necessarily involves additional parts and additional fabrication steps which contribute to the overall fabrication costs of the devices. The steel strap also requires a secondary tapping operation for accommodating the wall plate mounting screw.
The assembly method of these devices is a further source of problems. The body and cover, with the mounting strap held between them, are usually secured together by a fastening rivet or screw-like fastener which is inserted through the back of the receptacle body, through a clearance hole formed in the mounting strap and then force fit in a hole formed in the receptacle cover. To insure adequate holding power, close tolerances are required between the outer diameter of the rivet or screw-like fastener and the holes in the receptacle body and cover. Thus, if blisters are formed in the vicinity of these holes during molding or if the parts are warped in that vicinity, the resultant parts are susceptible to cracking when the fastner is installed. Further, since the only means of securing the parts together is the rivet or screw fastener, the attachment of the cover and body is vulnerable to loosening, resulting in a dangerous intermittant condition in, or total disconnection of, the electrical connections within the device.
A significant breakage problem has also been experienced in the course of installing receptacles. One common construction practice involves "dealing out" individual receptacles at each specific location where a receptacle is to be installed by actually dropping them onto the floor. Because of the brittle nature of the thermo-set materials used in the devices, the receptacles are susceptible to cracking or breakage (with the attendant loosening or disconnection of electrical connections) when they are handled in such fashion. Also, breakage can occur in normal usage after installation when, e.g., a user pulls on the electrical cable to remove the plug at some distance from the receptacle itself. Although thermo-plastic materials could be used to form the receptacle body and cover and reduce some of the breakage problems, they tend to be relatively expensive and, in any event, the mere substitution of materials would not eliminate the other drawbacks described herein.
Another disadvantage of conventional electrical outlet receptacles is the problem encountered when the wall opening cut to receive the receptacle is too large for one or both ends of the mounting strap to bear against the wall surface when the device is mounted to an electrical outlet box behind the wall. To compensate, electricians often rely on the wall plate mounting screw to hold the receptacle in place. Such installation results in what is called a "floating" installation, wherein the device mounting screws are not tightened all the way so the device can "float" relative to the outlet box. The only means for bracing the outlet receptacle against the inward force of insertion of a plug is the single wall plate mounting screw. (In a proper installation, of course, both ends of the mounting strap should abut the wall to brace the receptacle against the inward force of plug insertion.)
Such "floating" installations are undesirable because they require extra installation time. The electrician must judge how far to tighten down the mounting screws to accommodate the wallplate, yet allow enough slack to pull the device back against the wallplate. In addition, where non-metallic wall plates are used (particularly those commonly made of phenolic or urea), the wallplate can be cracked or broken by repeated insertion of plugs in a "floating" receptacle installation, since the force of insertion of the plug is sustained only by the wallplate screw.
It is therefore an object of the present invention to provide a new and improved electrical outlet receptacle which overcomes the foregoing drawbacks and is of rugged construction and capable of economical fabrication, particularly for residential grades. It is another object of the invention to provide a new and improved electrical outlet receptacle which can be fabricated essentially completely from thermo-plastic (including mounting strap portions) except for the electrical contacts/terminals and ground elements.
It is also an object of the invention to provide a new and improved electrical outlet receptacle having mounting means adapted to substantially reduce the possibility of "floating" installations. In addition, it is an object of the invention to enable incorporation of such mounting feature in outlet receptacles for various sized wallplates.
It is also an object of the present invention to provide a new and improved electrical outlet receptacle having a grounding system capable of automatically grounding the receptacle when it is mounted to a grounded metal electrical outlet box without requiring a metallic mounting strap and/or separate internal ground contacts to mate with the ground prong of a plug. It is a further object of the invention to provide such a receptacle device which also incorporates alternate grounding means for direct termination to the ground conductor of an electrical power cable.
It is yet another object of the present invention to provide an electrical outlet receptacle having a cover member and body which can be formed by simple two-part injection molding techniques. It is still another object of the invention to provide such a receptacle having a mounting strap formed integrally with the cover member to simplify fabrication and reduce the number of component parts for the complete device.
Further, it is an object of the present invention to provide a new and improved electrical outlet receptacle capable of fully automated assembly by the use of component parts which can be secured in place before the final assembly step. It is another object of the invention to provide such a receptacle device and method of assembly which obviates the need for using the usual rivet or screw-type fastener yet forms a securely assembled receptacle device.
Objects and advantages of the invention are set forth in part herein and in part will be apparent herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the structures, instrumentalities and combinations pointed out in the appended claims. Accordingly, the invention resides in the novel parts, structures, arrangements, combinations, and improvements herein shown and described.